In a strain of rats bred for their suseptibility to hypertension and stroke (Stroke-prone SHR) we observed a much higher incidence of cerebrovascular lesions when these animals were maintained on diet containing 15% protein as compared to rats receiving a diet containing 22% protein. The addition of NaCl to the drinking water exacerbated the incidence of stroke particularly in animals receiving a low protein diet. It is suggest that genetic and environmental (dietary) factors interact in a manner that is highly relevant to the incidence of cerebrovascular disease in this animal model.